Sold/carried by Knick Knack in Little Lamplight. Alternatively in Dashwood's safe in Tenpenny Tower. Quest reward from Herbert Dashwood, received for completing 'A Manhandled Manservant'. Jocko's Pop & Gas Stop, northwest of Tenpenny Tower and east of Girdershade. Quest reward from Moira in the 'The Wasteland Survival Guide' quest, after the Minefield portion of the quest. Below is a list with the locations of the schematics. However, finding more than three schematics will not give more benefit.
Or in the case of explosives the yield will be higher, ie. Finding multiple schematics will increase the starting condition of the weapon. You can find several schematics for the same weapon.
The schematic will show you which parts you need.
Once you locate a schematic you can view it in your Pip-Boy. To make a custom weapon you first have to find the schematic.
